Stable aqueous metallic flake dispersion using phosphated acrylic polymer dispersant

ABSTRACT

A graft copolymer dispersant (binder) having a weight average molecular weight of about 5,000-100,000 wherein: (1) the graft copolymer has a polymeric backbone formed by polymerizing ethylenically unsaturated monomers; (2) the graft copolymer has macromonomer side chains attached to the backbone at a single terminal point that have weight average molecular weights of about 1,000-30,000 and are formed from by polymerizing ethylenically unsaturated monomers in the presence of a cobalt chain transfer agent. The graft copolymer further contains about 2 to 70% by weight, based on the weight of the graft copolymer, of polymerized constituents having a phosphate moiety or phosphoric acid moleties that are polymerized into the backbone, the side chains, or both. The graft copolymer is neutralized with an inorganic base or an amine.

This is a division of application Ser. No. 08/294,002, filed Aug. 22,1994.

TECHNICAL FIELD

This invention relates to a stable aqueous metallic flake dispersionthat utilizes a phosphated acrylic polymer dispersant. In particularthis invention is directed to stable aqueous aluminum flake dispersionsthat utilizes a branched phosphated acrylic polymer

BACKGROUND OF THE INVENTION

The use of metallic flake pigments such as aluminum flake pigments incoating compositions used in particular for exterior finishes forautomobiles and trucks to provide the finish with metallic glamour iswell known. There are relatively few problems with the addition of thesemetallic flakes by conventional methods to solvent based coatingcompositions but in waterborne compositions, the metallic flake, inparticular, aluminum flake, reacts with water and any acid constituentspresent in the coating composition and the flake deteriorates and cancause the evolution of gas and finishes formed with such coatings have areduced brightness.

To avoid such problems, phosphated linear random polymers have beenused. Such polymers have been added to metallic flake containing coatingcompositions as shown in Frangou U.S. Pat. No. 4,675,358 issued Jun. 23,1987 and in Chang U.S. Pat. No. 5,104,922 issued Apr. 14, 1992. Thephosphated portion of the polymer provides passivation of the flake.Residual phosphoric acid groups attached to the polymer are neutralizedwith an amine or an inorganic base to disperse the polymer into water.These polymers must be sufficiently hydrophobic in order to associatewith the metallic flake which typically is an aluminum flake whosesurface area is hydrophobic. To obtain a balance of properties withthese polymers has been very difficult. If more passivation is neededfor the flake, the phosphated portion of the polymer is increased but atthe expense of the hydrophobic portion of the polymer which reduces thedispersibility of the polymer. On the other hand, if more dispersibilityis needed, the phosphated portion of the polymer is reduced butprotection provided to the flake is reduced proportionately. Optimumpassivation and dispersibility cannot be obtained since these propertiesof passivation and dispersibility of the polymer are being balancedagainst one another. These phosphated polymers offered some improvedprotection to metallic flake pigments against the evolution of gases anddid improve the stability of coating compositions formulated withmetallic pigments but additional improvements for long term stabilityand prevention of gassing are still required.

A polymeric dispersant is needed that will form an aqueous pigmentdispersion that is stable, will protect and not allow for thedeterioration of the metallic flake pigment, will not allow for theformation of gases and is compatible with a variety of polymeric filmforming binders conventionally used in water based coating compositionsand that will cure with the film forming binder to form a finish ofautomotive quality that does not deteriorate on weathering because ofadverse properties of the polymeric dispersant.

SUMMARY OF THE INVENTION

A pigment dispersion useful for forming aqueous coating compositionscontaining metallic flake pigment, an aqueous carrier and a phosphatizedgraft copolymer dispersant (binder);

wherein the graft copolymer has a weight average molecular weight ofabout 5,000-100,000 and contains about 20-80% by weight of a polymericbackbone and about 80-20% by weight of macromonomer side chains attachedto the backbone wherein

(1) the polymeric backbone is formed of polymerized ethylenicallyunsaturated monomers and

(2) the side chains are macromonomers that are attached to the backboneat a single terminal point and formed from polymerized ethylenicallyunsaturated monomers that are polymerized in the presence of a cobaltchain transfer agent and have a weight average molecular weight of about1,000-30,000;

wherein the graft copolymer contains about 2 to 70% by weight, based onthe weight of the graft copolymer, of polymerized constituents having aphosphate moiety and phosphoric acid moieties that are polymerized intothe backbone, the side chains or both and the polymer is neutralizedwith an inorganic base or an amine; and

the metallic flake pigment is present in a binder to pigment weightratio of least 10/100.

A process for making the dispersion, coating compositions containing thenovel dispersion, the graft copolymer and the process for making thegraft copolymer also are part of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The novel pigment dispersion is stable and in general is non-flocculatedor agglomerated and is compatible with a variety of polymeric filmforming binders that are conventionally used in waterborne coatingcompositions and in particular is compatible with acrylic polymers thatare widely used in waterborne coatings. The graft copolymer dispersantused in the pigment dispersion upon curing of the coating, generallyreacts with other film forming components of the coating composition andbecomes part of the film and does not cause deterioration of the filmupon weathering as may occur if it were an unreacted component of thefilm. The graft copolymer protects the metallic flake pigment andsubstantially reduces gassing caused usually by reaction of the metallicflake pigment with acidic components of the coating composition. Also,the freeze-thaw stability of the pigment dispersion is improved. Becausethe graft copolymer is an excellent pigment dispersant, the ratio ofcopolymer to pigment is less than is used with conventional dispersantsand by using less of the dispersant water sensitivity of the resultingfinish is reduced.

By using a graft copolymer to form the pigment dispersion rather than alinear random copolymer, an optimum copolymer composition can be formedwhich will provide maximum passivation of the flake and will adequatelydisperse the flake and form a stable dispersion and stable aqueouscoating composition which utilize the dispersion. The surface of themetallic flake is hydrophobic and either the backbone or the side chainsof the graft copolymer are formed from hydrophobic monomers which areattracted to the surface of the flake. Phosphate groups which passivatethe flake can be obtained by polymerizing glycidyl (meth) acrylate,meaning either glycidyl acrylate or glycidyl methacrylate, into thebackbone or side chains and subsequently reacting the glycidyl groupswith phosphoric acid or phosphorus pentoxide. Unreacted or residualphosphoric acid group are neutralized with amine or an inorganic basefor dispersion into water. The remainder of the graft copolymer can beadjusted to improve dispersibility of the flake and make the copolymermore compatible with other components of the binder to form a stabilizedpigment dispersion.

Another way to introduce phosphate groups into the polymer, is to form apolymer having reactive hydroxyl group for example, by forming thecopolymer with hydroxy alkyl methacrylates or acrylates and subsequentlyreacting the hydroxy groups with phosphorus pentoxide and neutralizingphosphoric acid groups with amine or inorganic base as above.

A number of parameters can be adjusted with a graft copolymer to form anoptimum dispersant which can not be accomplished with a linear polymer.The ratio of backbone to side chains can be adjusted, the molecularweight of the backbone or side chains can be increased or decreased, thephosphate content of the copolymer in either the side chains or backbonecan be adjusted and the hydrophobicity and hydrophilicity of thebackbone and side chains can be adjusted as needed to provide optimumpassivation and dispersibility. By using a graft copolymer rather than alinear polymer, a substantially wider range of copolymers can formulatedthat balance, hydrophilicity and hydrophobicity and phosphate content ofthe graft copolymer to form superior dispersions and coatingcompositions in comparison to the compositions than could be formed withlinear polymers.

The backbone of the graft copolymer can be hydrophobic in comparison tothe side chains or the backbone can be hydrophilic in comparison to theside chains. For example, if the backbone of the graft copolymer ishydrophobic, it is formed with a sufficient amount of hydrophobicmonomers to make the backbone hydrophobic in comparison to the sidechains. The backbone of such a graft copolymer is attracted to the flakeand passivates the flake and the side chains of the graft copolymer canbe hydrophilic sufficient to disperse the flake in water to form adispersion. Conversely, the backbone can be hydrophilic and the sidechain hydrophobic. Either the backbone or the side chains of the graftcopolymer can be formed from hydrophilic monomers which are attracted towater in the composition to disperse the flake in water. It is notnecessary that either the backbone or the side chains of thee graftcopolymer be formed from monomers that are entirely hydrophobic orhydrophilic but it is necessary that the backbone and the side chains behydrophobic or hydrophilic in comparison to each other. Also, it is notnecessary that the phosphate groups all be incorporated into thehydrophobic part of the graft copolymer but can be incorporated into thehydrophilic part of the polymer as well. Residual phosphoric acid groupswhen subsequently neutralized with either an amine or an inorganic baseaid in dispersing the polymer.

The graft copolymer preferably contains about 25-75% by weight ofpolymeric backbone and correspondingly about 75-25% by weight of sidechains. The graft copolymer has a weight average molecular weight ofabout 5,000-100,000 and preferably about 10,000-40,000.

Molecular weights are determined by Gel Permeation Chromatography usingpolystyrene as the standard and tetrahydrofuran as the carrier solvent.

The side chains of the graft copolymer are formed from macromonomersthat have a weight average molecular weight of about 1,000-30,000 andpreferably 2,000-15,000. The macromonomers are formed by polymerizingethylenically unsaturated monomers in the presence of a catalytic chaintransfer agent containing Co⁺² or Co⁺³. Then the graft copolymer isformed by polymerizing ethylenically unsaturated monomers and themacromonomers by using conventional polymerization catalyst. Theethylenically unsaturated monomers are polymerized with themacromonomers via the single terminal unsaturated group of themacromonomer.

The backbone of the resulting graft copolymer is of the polymerizedethylenically unsaturated monomers and the side chains are of themacromonomers polymerized into the backbone. Glycidyl (meth)acrylate isincorporated into either the backbone or side chains or both to providereactive glycidyl groups and then the glycidyl groups are reacted withphosphoric acid to provide the graft copolymer with pendant phosphategroups. The molar equivalents of glycidyl groups to acid groups is about1/1.

The following ethylenically unsaturated monomers are used to formhydrophobic polymeric segments of the graft copolymer: alkyl acrylatesand methacrylates having 1-18 carbon atoms in the alkyl group such asmethyl methacrylate, ethyl methacrylate, ethyl acrylate, propylmethacrylate, propyl acrylate, isopropyl methacrylate, isopropylacrylate, butyl methacrylate, butyl acrylate, pentyl methacrylate,pentyl acrylate, hexyl methacrylate, hexyl acrylate, 2-ethyl hexylmethacrylate, 2-ethyl hexyl acrylate, nonyl methacrylate nonyl acrylate,lauryl methacrylate, lauryl acrylate, stearyl methacrylate, stearylacrylate and the like; cycloaliphatic methacrylates also can be usedsuch as trimethylcyclohexyl methacrylate, isobutylcyclohexylmethacrylate, and the like; aryl methacrylates and acrylates also can beused such as benzyl methacrylate and benzyl acrylate. Otherpolymerizable monomers that can be used are isobornyl acrylate,isobornyl methacrylate, styrene, alpha methyl styrene, methacrylamideand methacrylonitrile.

The following ethylenically unsaturated monomers are used to formhydrophilic polymer segments of the graft copolymer: hydroxy alkylacrylate and methacrylates having 1-4 carbon atoms in the alkyl groupsuch as hydroxy methyl acrylate, hydroxy methyl methacrylate, hydroxyethyl acrylate, hydroxy ethyl methacrylate, hydroxy propyl acrylate,hydroxy propyl methacrylate, hydroxy butyl acrylate, hydroxy butylacrylate and the like. Other useful monomers are acrylamide,acrylonitrile nitro phenol acrylate, nitro phenol methacrylate,phthalimido methyl acrylate, phthalimido methacrylate, and the like.

In the preparation of the macromonomer to ensure that the resultingmacromonomer only has one terminal ethylenically unsaturated group whichwill polymerize with the backbone monomers to form the graft copolymer,the macromonomer is polymerized by using a catalytic cobalt chaintransfer agent that preferably contains a Co⁺² or Co⁺³ group. Typically,in the first step of the process for preparing the macromonomer, themonomers are blended with an inert organic solvent and a cobalt chaintransfer agent and heated usually to the reflux temperature of thereaction mixture. In subsequent steps additional monomers and cobaltcatalyst and conventional azo type polymerization catalyst such as2,2'-azobis(2-methylbutanenitrile) and2,2'-azobis(2,4'-dimethylpentanenitrile)2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile) are added andpolymerization is continued at about 100°-135° C. for about 4-8 hoursuntil a macromonomer is formed of the desired molecular weight.

Preferred cobalt chain transfer agents or catalysts are described inU.S. Pat. No. 4,680,352 to Janowicz et al and U.S. Pat. No. 4,722,984 toJanowicz and WO 87/03605, hereby incorporated by reference in theirentirety. Most preferred are pentacyanocobaltate (II or III),diaquabis(borondifluorodimethyl-glyoximato) cobaltate(II or III) anddiaquabis(borondifluorophenylglyoximato) cobaltate (II or III).Typically these chain transfer agents used at concentrations of about5-1000 ppm based on the monomers used.

One preferred macromonomer contains about 1-10% by weight of isobutylmethacrylate, 65-85% by weight 2-ethyl hexyl methacrylate and 10-30% byweight hydroxy ethyl methacrylate and has a lo weight average molecularweight of about 7,000-10,000. Another preferred macromonomer containsabout 35-45% by weight of isobutyl methacrylate, 35-45% by weight2-ethyl hexyl methacrylate and 15-25% by weight of hydroxy ethylmethacrylate and has a weight average molecular weight of about7,000-10,000.

After the macromonomer is formed as described above, optionally solventis stripped off and the backbone monomers are added to the macromonomeralong with additional solvent and polymerization catalyst. Any of theaforementioned azo type catalyst can be used as can other suitablecatalyst such as peroxides and hydroperoxides. Typical of such catalystare di-tertiary butyl peroxide, di-cumylperoxide, tertiaryamyl peroxide,cumenehydroperoxide, di(n-propyl) peroxydicarbonate, peresters such asamyl peroxyacetate, t-butyl peracetate and the like. Polymerization iscontinued at about 100°-135° C. for about 4-8 hours usually at thereflux temperature of the reaction mixture until a graft copolymer isformed having the desired molecular weight.

Typical solvents that can be used to form the macromonomer or the graftcopolymer are ketones such as methyl ethyl ketone, isobutyl ketone,ethyl amyl ketone, acetone, alcohols such as methanol, ethanol,isopropanol, esters such as ethyl acetate and butyl acetate, glycolssuch as ethylene glycol, propylene glycol, ethers such astetrahydrofuran, ethylene glycol mono butyl ether, aromatic solventssuch as toluene and xylene, nitro paraffins such as 1-nitropropane and2-nitropropane and the like.

After the graft copolymer is formed, phosphoric acid or phosphorouspentoxide and solvent are added and the reaction is continued at about50°-70° C. for 4-6 hours or until all the glycidyl groups or hydroxylgroups are reacted. The extent of reaction can be determined by makingacid no. measurements. The polymer is blended with flake to form adispersion in an organic solvent followed by neutralization with anamine or an inorganic base and then water is added to form an aqueousdispersion.

Typical amines that can be used include amino methyl propanol, aminoethyl propanol, dimethyl ethanol amine, triethylamine and the like. Onepreferred amine is amino methyl propanol and the preferred inorganicbase is ammonium hydroxide.

Particularly useful graft copolymers include the following:

A graft copolymer having a backbone of polymerized monomers ofstyrene/methyl methaerylate/butyl aerylate/glycidylmethacrylate/hydroxyethyl methacrylate in weight ratios of20/25/15/20/20, 30/20/15/20/15 and 20/25/25/20/10 and having a weightaverage molecular weight of about 14,000-18,000 and side chains of amacromonomer of polymerized monomers of isobutylmethacrylate/2-ethylhexyl methacrylate/hydroxyethyl methacrylate inweight ratios of 5/75/20 and 40/40/20 and having a weight averagemolecular weight of about 6,000-10,000. The glycidyl groups of theglycidyl methacrylate constituent are reacted with phosphoric acid on a1/1 molar equivalent basis. The graft copolymer can contain 20-80% byweight backbone and correspondingly 80-20% by weight side chains.

A graft copolymer having a backbone of polymerized monomers ofstyrene/methyl methacrylate/butyl acrylate/2-ethyl hexylmethacrylate/hydroxy ethyl acrylate having a weight average molecularweight of about 14,000-30,000 and side chains of a macromonomer ofpolymerized monomers of butyl methacrylate/glycidyl methacrylate.

A graft copolymer having a backbone of polymerized styrene/methylmethacrylate/butyl acrylate/2-ethyl hexyl methacrylate/hydroxy ethylacrylate/glycidyl methacrylate and side chains of macromonomers of butylmethacrylate/glycidyl methacrylate.

To form a metallic flake pigment dispersion, metallic flake pigment suchas aluminum flake is mixed with a solution of the phosphated acrylicgraft copolymer in an organic solvent and then an amine or an inorganicbase is added to neutralize the copolymer and water is added to form thedispersion. Conventional mixing is used to form the dispersion. Often anassociate thickener is added to aid in formation of a stable dispersion.The resulting pigment dispersion contains about 10-30% by weight ofpigment and dispersant and correspondingly about 90-70% by weight ofaqueous carrier and has a dispersant binder to pigment weight ratio ofat least 10/100 and preferably about 10/100 to 100/100.

In addition to the metallic flake pigment any of the conventionalpigments used in paints in particular waterborne paints can be used toform the pigment dispersion such as metallic oxides like titaniumdioxide, iron oxides of various colors, zinc oxide, carbon black, fillerpigments such as talc, china clay, barytes, carbonates, silicates and awide variety of organic pigments such as quinacridones, phthalocyanines,perylenes, azo pigments, indanthrones, carbazoles such as carbazoleviolet, isoindolinones, isoindolones, thioindigo reds,benzimidazolinones. Typically useful metallic flakes are aluminum flakewhich is preferred, bronze, nickel stainless steel flakes, pearlescentflakes, coated mica flakes such as mica flakes coated with finelydivided titanium dioxide and the like.

It may be desirable to add other optional ingredients to the pigmentdispersion such as antioxidants, flow control agents, rheology controlagents such as fumed silica, microgels UV stabilizers screeners,quenchers and absorbers.

Under some circumstances, it may be desirable to form pigmentdispersions by using the phosphated acrylic graft copolymer that do notcontain metallic flake pigments but any of the aforementioned nonmetallic flake pigments. Such pigments do not require passivation but itis expected that the dispersions would have excellent compatibility withthe aqueous paint composition and metallic flake dispersion made withthe phosphated graft copolymer.

Pigment dispersions of this invention can be added to a variety ofwaterborne coating compositions such as topcoats which may be monocoatsor basecoats of a clear coat base coat finish and may also be added toprimers and primer surfacers. These compositions preferably have anacrylic polymer as the film forming constituent and may containcrosslinking agents such as blocked isocyanate, alkylated melamines,epoxy resins and the like. Other film forming polymers can also be usedsuch as acrylourethanes, polyesters and polyester urethanes, polyethersand polyether urethanes that are compatible with the pigment dispersion.It is desirable to have the film forming polymer of the coatingcomposition be similar to the polymer of the pigment dispersion so thaton curing the polymer of the pigment dispersion will cure with thecoating polymer and become part of the film or coating.

The following examples illustrate the invention. All parts andpercentages are on a weight basis unless otherwise indicated. Molecularweights are determined by Gel Permeation Chromatography usingpolystyrene as the standard and tetrahydrofuran as the carrier solvent.

EXAMPLE 1

MACROMONOMER PREPARATION

A macromonomer was prepared by charging the following constituents intoa 2 liter flask equipped with a thermometer, agitator dropping funnels,reflux condenser and a means for maintaining a nitrogen blanket over thereactants:

    ______________________________________                                                               Parts by Weight                                        ______________________________________                                        Portion 1                                                                     Isobutyl methacrylate monomer (IBMA)                                                                   20.30                                                2-Ethylhexylmethacrylate monomer (2EHMA)                                                               304.90                                               Hydroxyethylmethacrylate monomer (HEMA)                                                                81.30                                                Butyl acetate            100.00                                               Toluene                  160.00                                               Portion 2                                                                     Diaquabis(borondifluorodiphenyl-glyoximato)                                                            0.03                                                 cobalt(II), Co(DPG-BF.sub.2)                                                  Methyl ethyl ketone      17.10                                                2,2'-azobis(2-methylbutanenitrile)                                                                     0.35                                                 Portion 3                                                                     Isobutyl methacrylate monomer                                                                          17.80                                                2 Ethylhexyl methacrylate monomer                                                                      267.50                                               Hydroxyethyl methacrylate monomer                                                                      71.40                                                2,2' azobis(2-methylbutanenitrile)                                                                     1.35                                                 Toluene                  86.50                                                Portion 4                                                                     Toluene                  32.00                                                2,2' azobis(2-methylbutanenitrile)                                                                     0.32                                                 Portion 5                                                                     T-butyl peracetate       0.20                                                 Butyl Cellosolve         31.40                                                Total                    1192.45                                              ______________________________________                                    

Portion 1 was heated was heated to its reflux temperature (about135°-140° C.). Portion 2 was added over a 5 minute period whilemaintaining the reaction mixture at its reflux temperature. Portion 3was added over 240 minute period while maintaining the reaction mixtureat its reflux temperature and the reaction mixture was held at itsreflux temperature for an additional 30 minutes. Portion 4 was addedover a 60 minute period while the reaction mixture was held at itsreflux temperature and then held at this temperature for an additional60 minutes. Portion 5 was added with mixing and the resultingcomposition was cooled.

The resulting macromonomer solution had a solids content of 64% and hada Gardner Holdt Viscosity of U and the macromonomer had a composition ofIBMA/2EHMA/HEMA 5/75/20. % Vinyl termination of the macromonomer asmeasured by TGA (Thermogravimetric Analysis) is in excess of 95%. Theweight average molecular weight of the macromonomer is 8400 and themacromonomer solution has a Gardner Holdt viscosity of U.

ACRYLIC GRAFT COPOLYMER A PREPARATION

The following constituents were charged into a 5 liter flask equipped asabove to form a graft copolymer solution:

    ______________________________________                                                               Parts by Weight                                        ______________________________________                                        Portion 1                                                                     Methyl amyl ketone       515.2                                                Macromonomer solution (prepared above)                                                                 1652.1                                               Portion 2                                                                     Styrene monomer (S)      211.5                                                Methyl methacrylate monomer (MMA)                                                                      264.3                                                Butyl acrylate monomer (BA)                                                                            158.6                                                Glycidyl methacrylate monomer (GMA)                                                                    211.5                                                Hydroxyethyl acrylate monomer (HEA)                                                                    211.5                                                T-butyl per acetate      37.7                                                 Total                    3262.4                                               ______________________________________                                    

Portion 1 was heated to about 125° C. and then Portion 2 was premixedand added over a 180 minute period while maintaining the reactionmixture at about 125° C. and tinder constant agitation. The reactionmixture was held at this temperature for an additional 120 minutes andcooled to room temperature

The resulting acrylic graft copolymer A solution had a solid content of64 % by weight and had a Gardner Holdt Viscosity of V and the branchedpolymer contains 50% macromonomer side chains and 50% backbone of acomposition of S/MMA/BA/GMA/HEA in a weight ratio of 20/25/15/20/20 andhad a weight average molecular weight of 16,000.

PHOSPHATED ACRYLIC GRAFT COPOLYMER A PREPARATION

The following constituents were charged into a 5 liter flask equipped asabove:

    ______________________________________                                        Portion 1                                                                     Isopropanol                  263.10                                           Aqueous 85% phosphoric acid solution                                                                       54.67                                            Portion 2                                                                     Branched acrylic polymer A solution (prepared above)                                                       1200.00                                          Isopropanol                  475.00                                           Methyl ethyl ketone          239.10                                           Total                        2231.87                                          ______________________________________                                    

Portion 1 was heated to 50° C. and then Portion 2 was added over a 90minute period while maintaining the temperature at 50° C. Thetemperature was increased to 70° C. and the reaction mixture was held atthis temperature for about 5 hours and cooled to room temperature. Theresulting phosphated branched acrylic polymer A solution had a GardnerHoldt Viscosity of A3, a solids content of 34.5% by weight and thecopolymer had a weight average molecular weight of 16,400.

PHOSPHATED ACRYLIC GRAFT COPOLYMER B SOLUTION

Prepared identically as above except the weight ratio of macromonomer tobackbone was 70/30.

PHOSPHATED ACRYLIC GRAFT COPOLYMER C SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Asolution except the weight ratio of macromonomer to backbone was 30/70.

PHOSPHATED ACRYLIC GRAFT COPOLYMER D SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Asolution except the macromonomer had the following composition:IBMA/2EHMA/HEMA in a weight ratio of 40/40/20.

PHOSPHATED ACRYLIC GRAFT COPOLYMER E SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Asolution except the backbone had the following composition:S/MMA/BA/GMA/HEA in a weight ratio of 30/15/15/20/20.

PHOSPHATED ACRYLIC GRAFT COPOLYMER F SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Asolution except the backbone had the following composition:S/MMA/BA/GMA/HEA in a weight ratio of 20/25/25/20/10.

PHOSPHATED ACRYLIC GRAFT COPOLYMER G SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Asolution except the backbone had the following composition:S/MMA/BA/GMA/HEA in a weight ratio of 30/10/20/30/10.

PHOSPHATED ACRYLIC GRAFT COPOLYMER H SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Asolution except the macromonomer had the following composition: BMA/GMAin a weight ratio of 80/20 and the backbone had the followingcomposition S/MMA/BA/2EHMA/HEA in a weight ratio of 30/15/25/25/5.

PHOSPHATED ACRYLIC GRAFT COPOLYMER I SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Asolution except the macromonomer had the following composition: BMA/GMAin a weight ratio of 80/20 and the backbone had the followingcomposition: S/MMA/BA/2EHMA/HEA/GMA in a weight ratio of30/15/25/15/5/10.

PHOSPHATED ACRYLIC GRAFT COPOLYMER J SOLUTION

Prepared identically as above phosphated acrylic graft copolymer Gsolution except that 1-nitropropane replaced methyl ethyl ketone in thephosphating step.

EXAMPLE 2

An aluminum flake pigment dispersion was prepared by charging thefollowing constituents into a mixing vessel agitated with an air mixer:311 parts of 1-pentanol, 133 parts n-butanol, 62 parts of phosphatedacrylic graft copolymer A solution (prepared in Example 1 ) and 283parts of aluminum paste (65% aluminum flake in mineral spirits). Theconstituents were agitated for 60 minutes to form a dispersion. 146parts of this dispersion was added to another mixing vessel and thefollowing constituents were added with constant mixing: 3 parts ofdimethyl ethanol amine, 1 part latex thickener (Henkel DSX-1550 acrylicassociative thickener) and mixed for 30 minutes, 93.5 parts deionizedwater, 214.3 parts acrylic copolymer latex, 85 parts of aleionizedwater, 0.85 parts of latex thickener (described above) and mixed for 1hour, 4.25 part of 5% aqueous ammonium hydroxide solution, 102 partsdeionized water, 4.25 parts "Acrysol" ASE-60 Thickener (acrylic acidcopolymer from Rohm and Haas)and 202 parts deionized water. Theconstituents were mixed for 60 minutes to form a dispersion.

The resulting dispersion had a weight solids ratio of phosphatedbranched acrylic polymer to aluminum flake of 10:100. A sample of thedispersion was drawn down on a glass panel dried and evaluated fordegree of flocculation and brightness as quantified by lightness at 2degrees from the vertical on a DuPont Colorimeter. A pint can of thedispersion was placed in an oven at 50° C. for one and two weeks andevaluated for aluminum flake passivation by checking for excessive gasbuild up in the can and loss of dispersion. The results of these testare shown in the following table.

A control aluminum flake dispersion identical to the above dispersionwas formed in which the phosphated acrylic graft copolymer was omittedand the dispersion was tested as above. The results are shown in thefollowing table.

A linear phosphated acrylic polymer of methyl methacrylate, butylacrylate, glycidyl methacrylate in a weight ratio of 38/37/25 having aweight average molecular weight of about 21,500 was prepared byconventional polymerization methods using conventional mercaptan and azocatalysts and phosphated with phosphoric acid in 1:1 GMA:phosphoric acidmolar equivalent ratio. An aluminum flake dispersion using the aboveconstituents and procedure was prepared with the exception that theabove linear polymer was used in place of the phosphated acrylic graftcopolymer. The dispersion was tested as above and the results are shownin the following table.

Phosphated acrylic graft copolymers E and F prepared in Example 1 wereeach formulated into aluminum flake dispersions as above except thepolymers E and F were each substituted for polymer A in each of thedispersions. Each of the dispersions was tested as above and the resultsare shown in the following table.

                  TABLE                                                           ______________________________________                                        Aluminum Flake Dispersion                                                                     Brightness Stability at 50° C.                         ______________________________________                                        Phosphated acrylic graft                                                                      120        1 week                                             copolymer A                                                                   Phosphated acrylic graft                                                                      141        >4 weeks                                           copolymer E                                                                   Phosphated acrylic graft                                                                      139        >4 weeks                                           copolymer F                                                                   Control - No phosphated                                                                       Not measured                                                                             1 hour gassing & loss                              acrylic copolymer present  of dispersion quality                              Linear phosphated acrylic                                                                     Not measured                                                                             <2 days                                            copolymer                                                                     ______________________________________                                    

The above results show that the phosphated acrylic graft copolymers ofthe invention provide better quality dispersions that are substantiallymore resistant to gassing when compared to the control in which nophosphated acrylic polymer was present and to a linear phosphatedacrylic polymer representative of the prior art.

We claim:
 1. A graft copolymer having a weight average molecular weightof about 5,000-100,000 and comprising about 10-80% by weight of apolymeric backbone and about 80-20% by weight of macromonomer sidechains attached to the backbone wherein(1) the polymeric backbone beinghydrophilic in comparison to the side chains and consists essentially ofpolymerized ethylenically unsaturated monomers and (2) the side chainsbeing hydrophobic in comparison to the backbone and consist ofmacromonomers that are attached to the backbone at a single terminalpoint and consist essentially of polymerized ethylenically unsaturatedmonomers that are polymerized in the presence of a cobalt chain transferagent and have a weight average molecular weight of about1,000-30,000;wherein the graft copolymer contains about 2 to 70% byweight, based on the weight of the graft copolymer, of polymerizedglycidyl (meth)acrylate monomers in the backbone and the glycidyl groupsbeing reacted with phosphoric acid or phosphorous pentoxide.
 2. Thegraft copolymer of claim 1 in which the graft copolymer comprises about25-75% by weight of macromonomer and correspondingly about 75-25% byweight of polymeric backbone and the graft copolymer has a weightaverage molecular weight of about 10,000-40,000.
 3. The graft copolymerresin of claim 2 in which the macromonomer is formed by polymerizing themonomers in the presence of a catalytic chain transfer agent containingCo⁺² or Co⁺³.
 4. The graft copolymer of claim 3 in which themacromonomer consists essentially of polymerized monomers selected fromthe group consisting of styrene, alkyl methacrylates, alkyl acrylateseach having 1-18 carbon atoms in the alkyl groups and hydroxy alkylmethacrylate or hydroxy alkyl acrylate monomers each having 1-4 carbonatoms in the alkyl groups and any mixtures thereof, a backbone ofpolymerized monomers selected from the group consisting of styrene,alkyl methacrylate, alkyl acrylate, each having 1-18 carbon atoms in thealkyl groups, hydroxy alkyl methacrylate or hydroxy alkyl acrylate eachhaving 1-4 carbon atoms in the alkyl group and any mixtures thereof andglycidyl methacrylate or glycidyl acrylate.
 5. The graft copolymer ofclaim 3 in which the macromonomer consists essentially of polymerizedmonomers selected from the group consisting of styrene, alkylmethacrylates, alkyl acrylates each having 1-18 carbon atoms in thealkyl groups and hydroxy alkyl methacrylate or hydroxy alkyl acrylatemonomers each having 1-4 carbon atoms in the alkyl groups and anymixtures thereof and glycidyl methacrylate or glycidyl methacrylate, abackbone of polymerized monomers selected from the group consisting ofstyrene, alkyl methacrylate, alkyl acrylate, each having 1-18 carbonatoms in the alkyl groups, hydroxy alkyl methacrylate or hydroxy alkylacrylate each having 1-4 carbon atoms in the alkyl group.
 6. The graftcopolymer of claim 3 in which the macromonomer consists essentially ofpolymerized monomers selected from the group consisting of styrene,alkyl methacrylates, alkyl acrylates each having 1-18 carbon atoms inthe alkyl groups and hydroxy alkyl methacrylate or hydroxy alkylacrylate monomers each having 1-4 carbon atoms in the alkyl groups andany mixtures thereof and glycidyl methacrylate or glycidyl methacrylate,a backbone of polymerized monomers selected from the group consisting ofstyrene, alkyl methacrylate, alkyl acrylate, each having 1-18 carbonatoms in the alkyl groups, hydroxy alkyl methacrylate or hydroxy alkylacrylate each having 1-4 carbon atoms in the alkyl group and anymixtures thereof and glycidyl methacrylate or glycidyl acrylate.